1. Field of the Invention
This invention relates to a fuel metering control system for an internal combustion engine.
2. Description of the Related Art
The application of adaptive control theory to internal combustion engines in recent years has led to the development of technologies for adaptively controlling the actual quantity of fuel drawn into the engine cylinders to the desired fuel quantity, as taught, for example, by Japanese Laid-Open Patent Application No. Hei 1(1989)-110,853.
The present assignee's Japanese Patent Application No. Hei 6(1994)-66,594 (Japanese Laid-Open Patent Application No. Hei 7(1995)-247,886) (filed in the United States on Mar. 9, 1995 under the Ser. No. 08/401,430) also teaches fuel metering control in an internal combustion engine using adaptive control. However, when actually installed in an internal combustion engine, fuel metering control systems utilizing adaptive control are unable to operate freely owing to fluctuations in available computation time caused by variations in engine speed and in performance limitations of the microcomputer used. Moreover, while the fuel metering control cycle is normally once per TDC (Top Dead Center), it takes about 8-12 TDCs after fuel injection to detect the control result (controlled variable). There is thus an 8 to 12 TDC dead time. Generally speaking, control performance decreases with increasing dead time of the controlled system. This is particularly true of adaptive control.